1. Field of the Invention
This invention relates to a composition containing a binder and a modifier. More specifically, this invention relates to a composition containing a binder and a modifier which is a novel material derived as a coproduct from the medium pressure depolymerization of nylon 6 carpet. The compositions are useful as road asphalt, roof membranes, molding compounds, and plastic lumber.
2. Brief Description of Related Art
Asphalt is commonly used as a roadway material due to its low material cost and ease of application. In general, maintenance is required to repair cracks and holes in the pavement, often at significant costs. This has become a major issue for our nation in recent years due to higher traffic volumes, increased loads and higher tire pressures. Clearly, improved overall performance grades of asphalt which will lead to a reduction in maintenance costs are desirable. The performance improvements, however, have to be achieved in a manner that does not increase significantly the base asphalt paving economics.
It is known that a variety of polymer additives, such as polyethylene and thermoplastic elastomers, can improve the level of field performance of asphalt. The use of polyethylene as a modifier improving rheological properties for paving asphalt has been disclosed in, for example, D. N. Little and G. Legnani, (1989). The use of polyethylene as a modifier for roofing asphalt to increase coating viscosity and hardness has been disclosed in, for example, U.S. Pat. No. 4,328,147. The addition of elastomers to asphalt has been shown to improve flow characteristics and reduce cracking of the asphalt, especially at low temperatures due to heavy loads. U.S. Pat. Nos. 4,547,399, 4,835,199, and 5,002,987 exemplify the use of elastomers in asphalt. U.S. Pat. No. 5,744,524 teaches a polymer-modified asphalt which further comprises a dispersing agent to generate a polymer modified asphaltic composition with good dispersion characteristics. A. Usmani (1996) teaches a carboxylated monomer/polymer additive to a filled, polypropylated asphalt to improve thermostability. Addition of elastomers, however, presents difficulties at higher use temperatures as the asphalt becomes sticky, and rutting occurs in high traffic areas of the roadway. Solutions to this problem are sought by adding graft copolymer resins comprising a rubbery polymeric substrate and a rigid polymeric superstrate, as described for example in U.S. Pat. No. 5,710,196.
Asphalt is an inexpensive thermoplastic and, therefore, the inclusion of costly polymer additives is economically unattractive despite the property gains observed. Therefore, polymer additives are as yet not widely used in asphalt paving despite the improvements they impart in pavement properties such as crack resistance and reduced rutting. The use of less costly plastic modifiers derived from waste polymer sources is an option being studied by a number of investigators, for example, in V. J. Peters and D. V. Holmquist (1992), and U.S. Pat. No. 5,702,199. The use of waste carpet material as a modifier for asphalt has been disclosed in U.S. Pat. No. 5,665,447 and in G. S. Gordon et al. (1993), and as a modifier for concrete in Y. Wang et al. (1993). None of these three disclosure teaches nor suggests the use of coproduct produced in medium-pressure depolymerization of nylon waste carpet as a modifier for compositions.
In this invention, the addition of coproduct, a unique blend of predominantly polypropylene (PP), styrene butadiene rubber (SBR) and calcium carbonate (CaCO3), leads to a significant improvement in the performance of the asphalt. The unique combination of the three main components results in a range of asphalt property enhancements that are not achievable by simple physical combination of the individual components. In addition, the coproduct, since it is derived from recycled carpet through a novel process, has a very favorable cost position compared to other polymer-based asphalt modifiers.
The solution to the problem is a composition comprising a binder and a residue wherein the residue comprises a blend of polypropylene, styrene butadiene rubber and calcium carbonate. The residue is a unique coproduct derived from the medium-pressure depolymerization of nylon 6 carpet, a novel process taught in commonly-assigned U.S. Pat. No. 5,681,952.
In one preferred embodiment, coproduct is mixed with hot asphalt as the binder. The level of coproduct added to the asphalt is between about 0.5 weight % (wt %) to about 80 wt %, more preferably between 2 wt % to 50 wt % and most preferably between 5 wt % to 30 wt %. This embodiment results in a significant reduction in the creep stiffness and improvement of the rheological properties at both high and low temperature in the resultant binder-residue composition compared to the binder alone. Addition of aggregate to this embodiment yields a composition useful for paving applications.
In another preferred embodiment, coproduct is mixed with a plastic as the binder. The level of coproduct added to the plastic is between about 0.5 wt % to about 80 wt %, more preferably between about 2 wt % to about 70 wt %, and most preferably between about 9 wt % to about 60 wt %.
In another preferred embodiment, coproduct is mixed with a thermoset polyester as the binder. The level of coproduct added to the plastic is between about 0.5 wt % to about 80 wt %, more preferably 2 wt % to about 50 wt %, and most preferably about 5 wt % to about 20 wt %.